exit(3) - f38

1exit(3)                    Library Functions Manual                    exit(3)
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NAME

6       exit - cause normal process termination
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <stdlib.h>
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14       [[noreturn]] void exit(int status);
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DESCRIPTION

17       The  exit()  function  causes  normal process termination and the least
18       significant byte of status (i.e., status & 0xFF)  is  returned  to  the
19       parent (see wait(2)).
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21       All  functions  registered with atexit(3) and on_exit(3) are called, in
22       the reverse order of their registration.  (It is possible  for  one  of
23       these  functions  to  use  atexit(3) or on_exit(3) to register an addi‐
24       tional function to be executed during exit processing; the  new  regis‐
25       tration  is  added to the front of the list of functions that remain to
26       be called.)  If one of these functions does not return (e.g., it  calls
27       _exit(2),  or  kills  itself with a signal), then none of the remaining
28       functions is called, and further exit processing (in particular, flush‐
29       ing  of  stdio(3) streams) is abandoned.  If a function has been regis‐
30       tered multiple times using atexit(3) or on_exit(3), then it  is  called
31       as many times as it was registered.
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33       All  open  stdio(3)  streams  are flushed and closed.  Files created by
34       tmpfile(3) are removed.
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36       The C standard specifies two constants, EXIT_SUCCESS and  EXIT_FAILURE,
37       that  may  be  passed  to exit() to indicate successful or unsuccessful
38       termination, respectively.
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RETURN VALUE

41       The exit() function does not return.
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ATTRIBUTES

44       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
45       tributes(7).
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47       ┌────────────────────────────────┬───────────────┬─────────────────────┐
48       │Interface                       │ Attribute     │ Value               │
49       ├────────────────────────────────┼───────────────┼─────────────────────┤
50       │exit()                          │ Thread safety │ MT-Unsafe race:exit │
51       └────────────────────────────────┴───────────────┴─────────────────────┘
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53       The exit() function uses a global variable that is not protected, so it
54       is not thread-safe.
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STANDARDS

57       C11, POSIX.1-2008.
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HISTORY

60       C89, POSIX.1-2001, SVr4, 4.3BSD.
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NOTES

63       The behavior is undefined if one  of  the  functions  registered  using
64       atexit(3)  and on_exit(3) calls either exit() or longjmp(3).  Note that
65       a call to execve(2) removes registrations created using  atexit(3)  and
66       on_exit(3).
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68       The  use of EXIT_SUCCESS and EXIT_FAILURE is slightly more portable (to
69       non-UNIX environments) than the use of 0 and some nonzero value like  1
70       or -1.  In particular, VMS uses a different convention.
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72       BSD  has  attempted  to  standardize exit codes (which some C libraries
73       such as the GNU C library have also  adopted);  see  the  file  <sysex‐
74       its.h>.
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76       After  exit(),  the  exit  status  must  be  transmitted  to the parent
77       process.  There are three cases:
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79       •  If the parent has set SA_NOCLDWAIT, or has set the  SIGCHLD  handler
80          to SIG_IGN, the status is discarded and the child dies immediately.
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82       •  If  the  parent was waiting on the child, it is notified of the exit
83          status and the child dies immediately.
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85       •  Otherwise, the child becomes a "zombie" process: most of the process
86          resources  are  recycled,  but a slot containing minimal information
87          about the child process (termination status, resource usage  statis‐
88          tics)  is retained in process table.  This allows the parent to sub‐
89          sequently use waitpid(2) (or similar) to learn the termination  sta‐
90          tus of the child; at that point the zombie process slot is released.
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92       If  the implementation supports the SIGCHLD signal, this signal is sent
93       to the parent.  If the parent has set  SA_NOCLDWAIT,  it  is  undefined
94       whether a SIGCHLD signal is sent.
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96   Signals sent to other processes
97       If the exiting process is a session leader and its controlling terminal
98       is the controlling terminal of the session, then each  process  in  the
99       foreground  process group of this controlling terminal is sent a SIGHUP
100       signal, and the terminal is disassociated from this  session,  allowing
101       it to be acquired by a new controlling process.
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103       If  the  exit of the process causes a process group to become orphaned,
104       and if any member of the newly orphaned process group is stopped,  then
105       a  SIGHUP  signal  followed  by  a  SIGCONT signal will be sent to each
106       process in this process group.  See setpgid(2) for  an  explanation  of
107       orphaned process groups.
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109       Except  in  the above cases, where the signalled processes may be chil‐
110       dren of the terminating process, termination of a process does  not  in
111       general  cause a signal to be sent to children of that process.  Howev‐
112       er, a process can use the prctl(2) PR_SET_PDEATHSIG  operation  to  ar‐
113       range that it receives a signal if its parent terminates.
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